The present invention relates to cementitious composites and, more particularly, to polymer particulate filled cementitious composites particularly well suited for roofing applications.
The preparation of low density concrete incorporating lightweight hydrophilic aggregates such as vermiculite, cork, slag and the like in a hydrophobic matrix such as a cement mixture are well known. The density and longevity of a cementitious composite are improved through the incorporation of polymeric foam particles, for example, polystyrene foam, as the lightweight aggregate. However, cementitious material, being hydrophilic, has inadequate adhesion to lightweight polymeric aggregates which are hydrophobic while the use of a binding agent in the cement mixture or a pre-coat of the hydrophobic polymeric particles with a binding agent to promote adhesion therebetween has long been contemplated.
The prior art is replete with binding agents including bituminous products, coal tars, mixtures of pitch with polymeric resins, shellac, polyvinyl acetate and the like. Additional additives such as metal ions have been added to binding agents to lessen the tack of the coated particles and lessen coalescence between particles. Prior art lightweight cementitious composites containing hydrophobic polymeric particulate have been limited to certain limitations owing to pumpability problems, cost, environmental concerns regarding binder leachants therefrom, and particle aggregation during mixing and application. Additionally, drying time of prior art composites is sufficiently long that such composites are susceptible to overnight washout before set. Thus, there exists a need for a lightweight cementitious composite material that addresses many of these limitations.
A lightweight cementitious composite material includes expanded synthetic polymer particulate having a particle size of between 0.0625 and 0.5 inches. A dispersant coating on said particulate suppresses electrostatic attraction between particulate particles. A matrix surrounds the particulate and is present from 0.25 to 1 pound per gallon of dispersant coated particulate. A process of applying a composite material to a substrate comprises the steps of: forcing a stream of dispersant into fluid communication with a stream of expanded synthetic polymer particulate having a particle size between 0.0625 and 0.5 inches to form a dispersed particulate; propelling said dispersed particulate and a matrix slurry through a tube to form a foamed combined stream where the matrix is present from 0.25 to 1 pound of said matrix per gallon of said dispersed particulate; and applying said foamed combined stream to the substrate.
A process for preparing a lightweight structure includes passing an expanded synthetic polymer through a plurality of meshes to remove a fraction therefrom having dimensions of less than 0.0625 inches and greater than 0.5 inches to obtain an expanded synthetic polymer particulate. A dispersion is then mixed with the expanded synthetic polymer particulate to form a lightweight dispersal. The dispersal is combined with a matrix at a ratio of between 0.25 to 1 pound of the matrix per gallon of dispersal. After the dispersal and the binder are combined, sufficient time is allowed for the matrix to set.